The present invention relates to an antenna arrangement for a multi-radiator base station antenna, the antenna having a feeding network based on air filled coaxial lines, wherein the coaxial lines preferably are an integrated part of the antenna reflector. The invention especially relates to such an antenna having a variable electrical elevation tilt angle. Electrical elevation tilt angle is henceforth termed tilt angle.
Antennas in telecommunication systems such as cellular networks today typically use multi-radiator structures. Such antennas make use of an internal feeding network that distributes the signal from a common coaxial connector to the radiators when the antenna is transmitting and in the opposite direction when the antenna is receiving. Typically the radiators are positioned in a vertical column. This arrangement reduces the elevation beam width of the antenna and by that increases the antenna gain. The antenna tilt angle is determined by the relative phases of the signals feeding the radiators. The relative phases can be fixed giving the antenna a predetermined tilt angle, or the relative phases can be variable if a variable tilt angle is required. In the latter case, the tilt angle can be adjusted manually or remotely.
Base station antennas with variable tilt angles using adjustable phase shifters already exist and are widely deployed, but their performance has so far been limited by the loss introduced in the internal feeding network and in the phase shifters. The feeding network is typically realized using coaxial cables having small dimensions in order to be bendable by hand in a small radius and favourable in price. Such cables introduce significant loss. The phase shifter is commonly realized in microstrip or stripline technology, known from WO 02/35651 A1, now U.S. Pat. No. 6,906,666. Phase shifting might be obtained by moving a dielectric part within this structure. The conductors typically have rather small dimensions and because of this they will introduce resistive losses. Typically such feeding networks, together with the phase shifter, introduce 1-3 dB loss. This will result in 1-3 dB lower antenna gain.
Improved antenna gain results in increased range, higher capacity and better quality of service for a base station, and will result in considerable savings and higher revenues for the operator.
The object of the present invention is therefore to provide a novel antenna with a variable tilt angle having a higher antenna gain than prior art antennas with variable tilt angle.
This object is obtained with an antenna having an adjustable differential phase shifter including a dielectric part that is arranged in the antenna and is movable longitudinally in relation to at least one coaxial line.